diff --git a/Doc/library/json.rst b/Doc/library/json.rst
--- a/Doc/library/json.rst
+++ b/Doc/library/json.rst
@@ -562,16 +562,17 @@ the last name-value pair for a given nam
 
    >>> weird_json = '{"x": 1, "x": 2, "x": 3}'
    >>> json.loads(weird_json)
    {'x': 3}
 
 The *object_pairs_hook* parameter can be used to alter this behavior.
 
 .. highlight:: bash
+.. module:: json.tool
 
 .. _json-commandline:
 
 Command Line Interface
 ----------------------
 
 The :mod:`json.tool` module provides a simple command line interface to validate
 and pretty-print JSON objects.
@@ -581,16 +582,20 @@ specified, :attr:`sys.stdin` and :attr:`
 
     $ echo '{"json": "obj"}' | python -m json.tool
     {
         "json": "obj"
     }
     $ echo '{1.2:3.4}' | python -m json.tool
     Expecting property name enclosed in double quotes: line 1 column 2 (char 1)
 
+.. versionchanged:: 3.5
+   The output is now in the same order as the input. Use the
+   :option:`--sort-keys` option to sort the output of dictionaries by their
+   key.
 
 Command line options
 ^^^^^^^^^^^^^^^^^^^^
 
 .. cmdoption:: infile
 
    The JSON file to be validated or pretty-printed::
 
@@ -608,11 +613,17 @@ Command line options
 
    If *infile* is not specified, read from :attr:`sys.stdin`.
 
 .. cmdoption:: outfile
 
    Write the output of the *infile* to the given *outfile*. Otherwise, write it
    to :attr:`sys.stdout`.
 
+.. cmdoption:: --sort-keys
+
+   Sort the output of dictionaries by their key.
+
+   .. versionadded:: 3.5
+
 .. cmdoption:: -h, --help
 
    Show the help message.
diff --git a/Doc/whatsnew/3.5.rst b/Doc/whatsnew/3.5.rst
--- a/Doc/whatsnew/3.5.rst
+++ b/Doc/whatsnew/3.5.rst
@@ -206,16 +206,23 @@ inspect
 ipaddress
 ---------
 
 * :class:`ipaddress.IPv4Network` and :class:`ipaddress.IPv6Network` now
   accept an ``(address, netmask)`` tuple argument, so as to easily construct
   network objects from existing addresses.  (Contributed by Peter Moody
   and Antoine Pitrou in :issue:`16531`.)
 
+json
+----
+
+* The output of :mod:`json.tool` command line interface is now in the same
+  order as the input. Use the :option:`--sort-keys` option to sort the output
+  of dictionaries by their key (contributed by Berker Peksag in :issue:`21650`).
+
 os
 --
 
 * :class:`os.stat_result` now has a :attr:`~os.stat_result.st_file_attributes`
   attribute on Windows.  (Contributed by Ben Hoyt in :issue:`21719`.)
 
 re
 --
diff --git a/Lib/json/tool.py b/Lib/json/tool.py
--- a/Lib/json/tool.py
+++ b/Lib/json/tool.py
@@ -6,37 +6,45 @@ Usage::
     {
         "json": "obj"
     }
     $ echo '{ 1.2:3.4}' | python -m json.tool
     Expecting property name enclosed in double quotes: line 1 column 3 (char 2)
 
 """
 import argparse
+import collections
 import json
 import sys
 
 
 def main():
     prog = 'python -m json.tool'
     description = ('A simple command line interface for json module '
                    'to validate and pretty-print JSON objects.')
     parser = argparse.ArgumentParser(prog=prog, description=description)
     parser.add_argument('infile', nargs='?', type=argparse.FileType(),
                         help='a JSON file to be validated or pretty-printed')
     parser.add_argument('outfile', nargs='?', type=argparse.FileType('w'),
                         help='write the output of infile to outfile')
+    parser.add_argument('--sort-keys', action='store_true', default=False,
+                        help='sort the output of dictionaries by their key')
     options = parser.parse_args()
 
     infile = options.infile or sys.stdin
     outfile = options.outfile or sys.stdout
+    sort_keys = options.sort_keys
     with infile:
         try:
-            obj = json.load(infile)
+            if sort_keys:
+                obj = json.load(infile)
+            else:
+                obj = json.load(infile,
+                                object_pairs_hook=collections.OrderedDict)
         except ValueError as e:
             raise SystemExit(e)
     with outfile:
-        json.dump(obj, outfile, sort_keys=True, indent=4)
+        json.dump(obj, outfile, sort_keys=sort_keys, indent=4)
         outfile.write('\n')
 
 
 if __name__ == '__main__':
     main()
diff --git a/Lib/test/test_json/test_tool.py b/Lib/test/test_json/test_tool.py
--- a/Lib/test/test_json/test_tool.py
+++ b/Lib/test/test_json/test_tool.py
@@ -1,43 +1,66 @@
 import os
 import sys
 import textwrap
 import unittest
 import subprocess
 from test import support
 from test.script_helper import assert_python_ok
 
+
 class TestTool(unittest.TestCase):
     data = """
 
         [["blorpie"],[ "whoops" ] , [
                                  ],\t"d-shtaeou",\r"d-nthiouh",
         "i-vhbjkhnth", {"nifty":87}, {"morefield" :\tfalse,"field"
             :"yes"}  ]
            """
 
+    expect_without_sort_keys = textwrap.dedent("""\
+    [
+        [
+            "blorpie"
+        ],
+        [
+            "whoops"
+        ],
+        [],
+        "d-shtaeou",
+        "d-nthiouh",
+        "i-vhbjkhnth",
+        {
+            "nifty": 87
+        },
+        {
+            "field": "yes",
+            "morefield": false
+        }
+    ]
+    """)
+
     expect = textwrap.dedent("""\
     [
         [
             "blorpie"
         ],
         [
             "whoops"
         ],
         [],
         "d-shtaeou",
         "d-nthiouh",
         "i-vhbjkhnth",
         {
             "nifty": 87
         },
         {
-            "field": "yes",
-            "morefield": false
+            "morefield": false,
+            "field": "yes"
         }
     ]
     """)
 
     def test_stdin_stdout(self):
         with subprocess.Popen(
                 (sys.executable, '-m', 'json.tool'),
                 stdin=subprocess.PIPE, stdout=subprocess.PIPE) as proc:
@@ -70,8 +93,16 @@ class TestTool(unittest.TestCase):
         self.assertEqual(out, b'')
         self.assertEqual(err, b'')
 
     def test_help_flag(self):
         rc, out, err = assert_python_ok('-m', 'json.tool', '-h')
         self.assertEqual(rc, 0)
         self.assertTrue(out.startswith(b'usage: '))
         self.assertEqual(err, b'')
+
+    def test_sort_keys_flag(self):
+        infile = self._create_infile()
+        rc, out, err = assert_python_ok('-m', 'json.tool', '--sort-keys', infile)
+        self.assertEqual(rc, 0)
+        self.assertEqual(out.splitlines(),
+                         self.expect_without_sort_keys.encode().splitlines())
+        self.assertEqual(err, b'')